Art of making paper pulp



Patented Aug. 31, 1926.

BEBTBAND-S. SUMMERS, OF PORT HURON, MICHIGAN.

ART OF MAKING PAPER PULP.

Io Drawing. Application filed July 9, My invention relates more particularly to an improvement in the so-called kraft process. This process is an alkaline process inwhich the material is subjected to a liquor containing primarily caustic soda and sulphide of soda. In the digestion of wood by this liquor, obnoxious odors arise due to mercaptans being formed which pollute the air surrounding the works. It is also a peculiarity of the kraft pulp that While it makes a very strong pliable paper it is brown in color and is very diflicult to bleach and when bleached losses considerable of its characteristic qualities.

I have discovered that phosphoric acid and its compounds which are soluble in hot strong caustic liquor have the peculiar effect when added to the liquor of greatly lessening or obviating the odor arising from-this process and ofrendering the resultant pulp much more easily bleached. The pulp is usually stronger and more pliable. By my. improved process I am able to produce a fully bleached pulpcapable of being blended in high grade white sheets and at'thesame time preserving the valuable qualities of kratt pulp. I prefer to use an alkaline phosphate either the acid phosphate of sodium or the full metallic sodium phosphate as it is readily obtainable on the market at a reasonableprice. A quarter of 1% of phosphoric acid by Weight of the moist chips is suflicient to bring about these results. However, I do not confine myself to this proportion. The quality of the pulp may be changed by varying the relative proportion of the sulphur and phosphoric compounds in the liquor, the amount of phosphate to be used depending upon the paper which is to be made from the pulp'produced.

I will now give an example of the commercial operation of my process. In a digester containing about 800 cubic feet of .tive .alkali per cubic 1924. Serial R0. 724,974.

liquor I introduce about 300 cubic feet of white liquor running about 7 pounds of acfoot. To this I-add about 500 cubic feet of black liquor from a previous cook and as the chips are being charged into the digester I usually sprinkle from to 100 pounds of phosphate figured as tri-sodic phosphate. I prefer to cook the batch from 2% to 3 hours reaching a maximum temperature of 180 centigrade. Such an operation produces in the neighborhood of 3 tons of the soft. pliable pulp capable of being bleached to full White. Instead of using tri-sodium phosphates other compounds containing phosphoric acidmay be employed. t

I claim:

-1. A process of producing kraft pulp which'consists in digesting the fiber in kraft liquor containing phosphoric acid compounds.

2. A process of producing kraft pulp which consists in digesting the fiber in kraft liquor containing a soluble phosphate.

3. A process of producing a kraft which consists in subjecting vegetable terial to the action of a solution containing pulp a caustic alkali, a sulphate of an alkali metal and a phosphate.

4. A process for producing bleached kraft pulp which consists first in digesting the vegetable material in a kraft liquor to which phosphoric acid or a salt thereof has been added and then subjecting the pulp to a bleaching operation substantially as described.

5. A process for making bleached kraft pulp which consists in cooking the material in a kraft liquor containing a soluble phosphate and then subjecting the resulting pulp to a bleaching operation substantially. as described. Y

BERTRAND S. SUMMERS. 

